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In-Utero Guide

By Kristine Ziwica for Your Baby Today

Pregnancy is indeed a scientific marvel: A cluster of cells evolves into a new life in just 280 days. But if you're an expectant parent, you're no doubt wondering, "What's going on in there?" Find the answers below with a week-by- week guide to your baby's fetal development. (Since doctors consider pregnancy a 40-week affair starting with the first day of your last period, your pregnancy really "begins" two weeks before you conceive.)

By Kristine Ziwica for Your Baby Today

Pregnancy is indeed a scientific marvel: A cluster of cells evolves into a new life in just 280 days. But if you're an expectant parent, you're no doubt wondering, "What's going on in there?" Find the answers below with a week-by- week guide to your baby's fetal development. (Since doctors consider pregnancy a 40-week affair starting with the first day of your last period, your pregnancy really "begins" two weeks before you conceive.)

Week 1:
You get your period.

Week 2:
While an egg ripens in one of your two fallopian tubes, the uterus starts to form a lining of blood-rich tissue.

Week 3:
Conception. Only one of the thousands of sperm that have traveled through the fallopian tubes breaks through the egg's protective barrier to form a zygote. The cells start to divide into a small cluster as they travel down the fallopian tube towards the uterus.
Size: .006 inches
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